This invention is related to the liquid-phase alkylation/transalkylation of aromatic hydrocarbons, particularly the alkylation/transalkylation of benzene and substituted benzenes to form ethylbenzene.
Various processing schemes comprising alkylation and/or transalkylation reactions are known to produce monoalkylaromatic products such as ethylbenzene in high yields. However, existing processes are not without problems including the production of undesirable by-products. For example, the production of unwanted xylenes is a particular problem in the production of ethylbenzene in the vapor phase commercial process using ZSM-5 zeolites. Another problem with existing processes concerns the use of Friedel Crafts catalysts such as solid phosphoric acid or aluminum chloride. The phosphoric acid catalysts generally require the use of a water co-feed which produces a corrosive sludge by-product. Problems concerning the sludge by-product can be avoided by the use of zeolite catalysts.
The use of large pore zeolite catalysts in the alkylation of aromatic hydrocarbons is known in the art. Early catalysts were made by simple exchange of the zeolite with a metal salt. For example, U.S. Pat. No. 2,904,607 to Mattox refers to the use of a crystalline metallic aluminosilicate having uniform pore openings of about 6 to 15 angstroms in the alkylation of aromatic hydrocarbons with an olefin. Zeolite alkylation and/or transalkylation catalysts containing a combination of metal and hydrogen sites are well known. U.S. Pat. No. 3,251,897 to Wise describes liquid phase alkylation in type zeolites containing rare earth and hydrogen. Wang
et al., Journal of Catalysis, 24, 262-271 (1972) describe Y zeolites containing a combination of aluminum and hydrogen that have activity for toluene disproportionation.
Despite these teachings, Type Y zeolites have not been generally used in commercial alkylation of aromatic hydrocarbons, particularly in the production of ethylbenzene. A major problem relating to these catalysts is low activity. An additional problem concerns lack of stability, that is, the loss of crystallinity when a catalyst containing exchanged (i.e. cationic) aluminum and/or hydrogen is exposed to water vapor above 400.degree. C. This means that the catalyst cannot be effectively regenerated. One approach to avoiding this problem is to use a non-metal stabilized Y zeolite. Such catalysts are typically prepared by partial ammonium ion exchange, steam calcination and further ammonium ion exchange. A final heat treatment drives off ammonia gas and leaves an activated hydrogen form of the zeolite. Such catalysts are discussed in U.S. Pat. Nos. 3,449,070 to McDaniel et al.: 3,493,519 to Kerr et al.: 3,293,192 to Maher et al.: 3,354,077 to Hansford: 3,929,672 to Ward: and 3,641,177 to Eberly et al. While these catalysts possess adequate thermal and hydrothermal stability, their catalytic properties are not stable as selectivities decrease significantly with relatively few regeneration cycles, apparently related to the continued shrinkage of the unit cell size.
Thus, Y zeolite catalysts in the hydrogen form are not stable and possess low activity. Rare earth exchanged Y zeolites are stable, but again possess insufficient activity. Non-metal stabilized Type Y zeolites are also stable, but possess selectivities that decline when regenerated. There remains a need for an effective process for the preparation of alkylated aromatics such as ethylbenzene utilizing a stable catalyst having good activity and selectivity.